To save channel capacity and storage space, considering that human ears are less sensitive to high frequency information than to low frequency information of an audio signal, the high frequency information is usually cut, resulting in decreased audio quality. Therefore, a bandwidth extension technology is introduced to reconstruct the cut high frequency information, so as to improve the audio quality. As the rate increases, with coding performance ensured, a wider band of a high frequency part that can be coded enables a receiver to obtain a wider-band and higher-quality audio signal.
In the prior art, in a condition of a high rate, a frequency spectrum of an input audio signal may be coded in a full band by using the bandwidth extension technology. A basic principle of the coding is: performing band-pass filtering processing on the input audio signal by using a band pass filter (BPF) to obtain a full band signal of the input audio signal; performing energy calculation on the full band signal to obtain an energy Ener0 of the full band signal; coding a high frequency band signal by using a super wide band (SWB) time band extension (TBE) encoder to obtain high frequency band coding information; determining, according to the high frequency band signal, a full band linear predictive coding (LPC) coefficient and a full band (FB) excitation signal that are used to predict the full band signal; performing prediction processing according to the LPC coefficient and the FB excitation signal to obtain a predicted full band signal; performing de-emphasis processing on the predicted full band signal to determine an energy Ener1 of the predicted full band signal that has undergone de-emphasis processing; and calculating an energy ratio of Ener1 to Ener0. The high frequency band coding information and the energy ratio are transmitted to a decoder, so that the decoder can restore the full band signal of the input audio signal according to the high frequency band coding information and the energy ratio, and restore the input audio signal.
In the foregoing solution, the input audio signal restored by the decoder is apt to have relatively severe signal distortion.